The Brushless DFIG, also known as the Brushless Doubly-Fed Machine (BDFM), is one of a class of doubly-fed generators. Doubly-fed generators are machines with two accessible three phase windings to/from which electrical power can be fed/extracted. Generally, one winding is connected to the mains or grid and therefore has a fixed frequency, and the other is supplied from a fractionally rated power electronics converter.

The Brushless DFIG is an attractive type of doubly-fed generator. The key to the machine is the use of two stator windings of different pole numbers in a single frame, chosen so that there is no direct coupling between them, in combination with a special form of rotor which can couple both fields. The most significant features of the Brushless DFIG are that a) it is brushless in operation, b) it utilises a fractionally rated converter, and c) it shows greater compatibility with grid codes than the conventional DFIG, thereby providing substantial economic benefits. The Brushless DFIG is particularly attractive as an alternative replacement for doubly-fed slip-ring induction generators (DFIGs) in wind power plants, as brushless operation reduces the maintenance requirements and increases reliability. These advantages will become even more significant as more wind turbines are built offshore. The brushless doubly-fed machine can also be used as a motor in variable speed drive applications, making it the ideal choice in pumping, as well as many other applications.